1. Field of the Invention
The present invention pertains to plastic containers for beverages, particularly carbonated soft drink products and the like. More specifically, the invention relates to a blow molded plastic container whose shoulder portion comprises as an integral part thereof, a plurality of rib-like protrusions. These rib-like protrusions, which are outwardly-extending, are configured using multiple radii of curvature such that they may be successfully incorporated into even thin wall shoulder portions of the type found in commonplace non-returnable containers, and will furthermore remain intact even when such containers are under internal pressurization. The protrusions subject of the instant invention have the practical effect of lending improved grip and manual handling characteristics to the container, as well as providing mechanical reinforcement to the shoulder portion.
2. Description of the Prior Art
The use of plastic containers to package beverages, especially carbonated soft drink products, has been remarkably successful since such containers were first introduced in the 1970s. The widescale application of these containers stems primarily from the fact that the plastic material from which they are made, which materials are invariably thermoplastics, most especially polyesters such as polyethylene terephthalate (PET), can be biaxially oriented. Biaxial orientation involves aligning the polymer chains in two directions, the consequence being closer, more orderly packing of material. The practical benefits of this phenomenon are two fold: first, containers thus oriented can be produced with thin walls, often as a direct result of the orienting process itself; secondly, the mechanical strength and gas barrier properties of these thin-wall containers increases dramatically upon biaxial orientation. The overall result is a container that is light weight, yet extremely robust.
While it is known to fabricate biaxially oriented containers in any number of ways, the most commercially important are those which employ stretch blow molding techniques. These techniques generally utilize a preform or parison, typically produced by way of injection molding, which is heated, or cooled as the case may be, to at or near the glass transition temperature of the material. When at this temperature, the preform is placed into a blow mold wherein it is stretched longitudinally by a stretch rod and expanded horizontally by air or other operating gas pressure. The product is a container whose body and shoulder portions have relatively thin walls and are biaxially oriented.
Although the thin wall construction of biaxially-oriented containers is advantageous overall, there are, nevertheless, certain drawbacks to the same. For example, the thin nature of the wall manifests little, if any, tolerance for a topographical configuration that is other than smooth, uniform and continuous. Thus even though it may be desirable to provide alterations or embellishments to the wall, it has been difficult, if not impossible, to do so without adversely affecting the mechanical integrity of the same, especially where the container is under conditions of stress, such as caused by the internal pressurization associated with the packaging of carbonated soft drinks.
Of the efforts made in this regard are those directed to placing inwardly directed ridges or ribs in the shoulder portion of such containers in order to improve grip and the consumer's ability to hold and handle the container. Despite the benefits such a feature would offer, it has not been possible to implement the same in a practical manner, much less a commercially acceptable one, in thin wall non-returnable containers. The attempts made in this regard have generally relied upon an inward rib configuration having but one radius of curvature, which type of configuration has typically resulted in a container having areas of unusually high stress at juncture points between the rib or ridge and the shoulder portion, which circumstance, under conditions of internal pressurization, can lead to container failure. More commonly, however, these attempts have resulted in ribs or ridges that evert, distort or deform, either in whole or in part, under conditions of internal pressurization.
The art thus recognizes a continuing need to develop a convenient and practical design for a rib-like protrusion which will not detract from the mechanical integrity of the container and will remain physically and visually intact upon pressurization.